In a communication field, specifically in a wireless communication field, SCBT (single-carrier block transmission) in which DFT (discrete Fourier transform) and IDFT (inverse DFT) are performed on a transmission side or a reception side and a single carrier signal is processed in a block unit is actively considered. The SCBT realizes high frequency utilization efficiency equivalent to that of a multi-carrier transmission system represented by OFDM (orthogonal frequency division multiplexing). Moreover, the SCBT has low peak power and high transmission power efficiency since a base of the SCBT is a single carrier signal. Note that in the following, PAPR (a peak-to-average power ratio) that is a ratio of a peak to average power is an index of a peak power characteristic. Also, the SCBT has multi-path resistance equivalent to that of OFDM since FDE (frequency-domain equalization) is performed on a reception side to thereby compensate for frequency distortion due to a multi-path transmission channel.
The SCBT is also called SC-FDE (single carrier-FDE), SC-FDMA (single carrier-frequency division multiple access), SC-OFDM (single carrier-OFDM), or DFT-Spread OFDM.
On the other hand, in a wireless communication system including a plurality of transmission antennas, called a MISO (a multiple-input single-output) system or a MIMO (multiple-input multiple-output) system, a several transmission diversity methods to improve transmission quality are proposed. In the following, a conventional transmission diversity method that can be applied to SCBT will be described. In order to simplify a description, a transmission diversity method of transmitting one signal stream from two transmission antennas that are a transmission antenna #1 and a transmission antenna #2 will be described as an example in the following description. However, a similar technology is also disclosed in a case where three or more transmission antennas are included.
As a simple transmission diversity method, a delay diversity technology is disclosed in Non Patent Literature 1. In the delay diversity technology disclosed in Non Patent Literature 1, a signal stream is transmitted from a transmission antenna #1 and a signal stream identical to the signal stream transmitted from the transmission antenna #1 is delayed and transmitted from a transmission antenna #2. Also, in Patent Literature 1, a CDD (cyclic delay diversity) technology in which a signal stream transmitted from a transmission antenna #2 is subjected to a cyclic delay in an IDFT block and transmitted is disclosed. When the delay diversity technology or the cyclic delay diversity technology is used, it is observed on a reception side that signal streams equivalently pass through a multi-path transmission channel with a delay. Thus, a multi-path diversity effect is acquired. Also, since a signal transmitted from a transmission antenna #2 is the same as a signal transmitted from a transmission antenna #1 and is only delayed, there is an advantage that transmission power efficiency can be kept without deterioration of a PAPR characteristic of a transmission signal waveform.
In Non Patent Literature 2, an STBC technology using STBC (space-time block code) is disclosed. In the STBC technology disclosed in Non Patent Literature 2, temporally-successive two blocks are a time block #1 and a time block #2. In the time block #1, signal streams are spread to two transmission antennas and are transmitted simultaneously. In the time block #2, the signals transmitted in the time block #1 are switched between the transmission antennas, and complex conjugate and sign inversion of a positive/negative sign with respect to the one transmission antenna only are performed. The above-described signal processing in the transmission means that orthogonal coding is performed in two dimensions of time and space on a transmission side and is generally called Alamouti coding. On a reception side, it is possible to easily perform decoding by performing linear combination of two received time blocks by using transmission channel information. Accordingly, diversity gain for the number of transmission antennas, that is, transmission full diversity is acquired.
In Non Patent Literature 3, unlike the above-described STBC that is orthogonally coded in two dimensions of space and time, an SFBC technology using SFBC (space-frequency block code) that performs similar coding in two dimensions of space and a frequency is disclosed. On the premise of OFDM and on the assumption that a frequency variation in a transmission channel between adjoining two sub-carriers can be ignored, in the SFBC technology, signal switching, complex conjugate, and sign inversion are performed in two transmission antennas between two adjoining sub-carriers in one time block. Accordingly, in the SFBC technology, there is an advantage that transmission full diversity is acquired similarly to the STBC technology and that time variation resistance of a transmission channel is high compared to the STBC technology since the coding is performed in the one time block. This SFBC technology can be applied not only to OFDM but also to the SCBT technology.
In Non Patent Literature 4, with respect to the SFBC technology disclosed in Non Patent Literature 3, an SFBC technology for SCBT with which technology PAPR of a transmission time waveform is not deteriorated at all by successful utilization of a property of discrete Fourier transform is disclosed. Also, in Patent Literature 2, in an SFBC technology similar to that in Non Patent Literature 4, a technology of coding in a time domain is disclosed.